It could be the latest Windows update is somehow breaking Firefox under certain circumstances (TBD).

Hi. it could be your A/V but you should disable AdBlock as it gets it's lists from the same place as2018-07-13T15:01:49-07:00Pkshadowhttps://support.mozilla.org/it/questions/1225703#answer-1132817

Hi. it could be your A/V but you should disable AdBlock as it gets it's lists from the same place as Adblock Plus does. Adblock Plus blocks more, so is really a conflict.
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So let's start here :
Try Firefox Safe Mode to TEST &amp;amp; see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

Click the menu button
, click Help
and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.

On Mac: Hold the option key while starting Firefox.

On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode(you may need to specify the Firefox installation path e.g. /usr/lib/firefox)